The objectives of this study are to define the etiology, epidemiology and clinical course of acute viral myopericarditis and the nature, frequency and pathogenesis of its chronic sequella especially congestive cardiomyopathy. The long-term goal is to assess the public health significance of viral myopericarditis and its sequella and the necessity and potential for control and improved therapy. Acute and convalescent sera submitted to this laboratory from patients with clinically diagnosed myopericarditis will be tested by microneutralization for a greater than or equal to 4-fold antibody rise and by counterimmunoelectrophoresis for the presence of immunoglobulin M anitbodies to Coxsackievirus B types 1-5. Mycoplasmal and other viral etiologies will also be explored. Patients with confirmed etiologic and clinical diagnosis will be followed systematically to determine the frequency and nature of recurrent or continuing disease. Conversely, patients with congestive cardiomyopathy will be studied for evidence of a viral etiology. Evidence obtained to date indicates that the group B Coxsackieviruses are the primary pathogens of acute myopericarditis, that the incidence of chronic or recurrent sequella is at least 25 percent and that aberrant immune response precipitated by the viral infection is important in pathogenesis. The confirmation and expansion of these data will be undertaken in this study.